Much attention has been devoted recently to the synthesis, characterization, and reactivity of well-defined macromonomers of various kinds. This interest in macromonomers stems from their utility as intermediates in the preparation of graft copolymers. These copolymers have many potential applications in areas of coatings and molding compositions.
Certain prior art macromonomers are capable of copolymerization with ethylene and lower alpha-olefins such as propylene.
A variety of methods for preparing certain classes of styrene, substituted styrene, butadiene, and substituted butadiene macromonomers are known in the art.
Patents of Milkovich (U.S. Pat. Nos. 3,786,116, 3,832,423, 3,842,059, and 3,862,267) teach how to make certain classes of vinyl terminated polystyrene and polybutadiene macromonomers and how to use these macromonomers to form copolymers with other ethylenically unsaturated monomers.
In teaching how to make his macromonomers, Milkovich discloses (U.S. Pat. No. 3,842,059 column 11, line 30 through column 15, line 17) that "living" anions formed in anionically catalyzed polymerization processes can be reacted with a "terminating" agent to yield the macromonomer. The terminating agent is difunctional. One of the functional groups reacts with and terminates the living anion. The other functional group is a vinyl group capable of reacting with other ethylenically unsaturated monomers in subsequent graft copolymerizations. While Milkovich acknowledges the possibility of "certain deleterious side reactions" and proposes the use of "capping" agents to minimize such reactions (U.S. Pat. No. 3,842,059 column 13, line 47 through column 14, line 12), he fails to recognize that the vinyl group in some of his terminating agents are also capable of anionic polymerization. In these cases, branching reactions can take place during the termination reaction which broaden the molecular weight distribution and increase the polydispersity of the macromonomer and can result in loss of reactive sites. Such branching reactions are disclosed by Bronn et al. (U.S. Pat. No. 4,857,615), Silver et al. (U.S. Pat. No. 4,857,618), and Martin (U.S. Pat. Nos. 4,080,400, 4,148,838, and 4,273,896). The vinyl groups of Milkovich terminating agents [U.S. Pat. No. No. 3,842,059, column 12, terminating agents (h), (i), and (j)] are capable of anionic polymerization during termination and thus are capable of producing branched macromonomers with increased polydispersities.
In teaching how to use his macromonomers, Milkovich discloses (U.S. Pat. No. 3,842,059, column 4, lines 44 through column 5, line 3, and column 21, lines 1-41) that his macromonomers can be polymerized using free-radical, anionic, cationic, condensation, and coordination catalysts. He further discloses that ZN catalysts can be used to copolymerize C.sub.2 to C.sub.18 alpha-olefins with other ethylenically unsaturated monomers (U.S. Pat. No. 3,832,423, column 3, lines 58-68; U.S. Pat. No. 3,842,059, column 18, lines 28-35; and U.S. Pat. No. 3,862,267, column 4, lines 43-53). However, Milkovich only exemplifies Ziegler-Natta (ZN) graft copolymerization of macromonomers with alpha-olefins below C.sub.4.
The prior art macromonomers of Milkovich which polymerize under free radical conditions to form copolymers with, for example, acrylate monomers, are unreactive in ZN graft copolymerizations.
Graft copolymers derived from cationically polymerizable isobutylene-derived macromonomers are described in U.S. Pat. No. 4,327,201. The patentees' disclosure of ZN polymerizable monomers is limited to olefins of four carbon atoms or less in the repeat unit.